[xsl] How to use generate-id() inside an xsl:function without a node available?

This seems an obvious question to ask, but I couldn't find anything on
the net (but more often than not, it is a matter of wrong keywords, I am
sure). The issue is this: I have a function that generates some nodes
based on some strings and these nodes must receive a unique ID/IDREF
value. Normally, one would use generate-id(), but inside a function (or
inside anything that does not have a context node), generate-id() will fail.

My question: how can I create unique identifiers without a node in sight?

My original function is a bit larger (ahum, counted > 100 lines today,
time for refactoring...) and creates some SVG objects that reference one
another, which is why I must make sure the ID for referencing the
xlink:href attributes are unique within the document. Don't let the SVG
and XLink upset or distract you, I just mention it to explain my use-case.

And no, there's no way that there will be a node in sight (it is really
disconnected from the source document). Yes, I can use different
techniques than xsl:function if needed (of course). Oh, and before I
forget: I can do so with extension functions or assignable variables
(saxon), but I'd rather not to.

Any ideas? It seems easy enough, but I couldn't find any (quick)
resolutions.